Sen. Rand Paul upped the ante Monday in his bid to secure a vote on cutting off aid to Pakistan, threatening to delay the Senate's quick escape planned for later this month.

In a letter to Senate Majority Leader Harry Reid (D-Nev.), the Kentucky Republican called for an immediate vote to end U.S. foreign aid to the country.

Paul is attempting the procedural gambit in an effort to secure the release of Shakil Afridi, a Pakistani doctor who provided assistance to U.S. intelligence efforts that led to the killing of Osama bin Laden.

"As you know, the number of work days in the 112th Congress is dwindling, and Congress may break for the November election as soon as next week," Paul wrote. "Because of the urgency of seeing that Dr. Afridi is freed, I am prepared to pursue any and all means to secure a vote on my bill immediately, including objecting to other Senate business and recessing the Senate for the election."

That the letter comes on the eve of the 11th anniversary of 9/11 might be a coincidence of the Senate calendar, but it could give Paul's effort some momentum.

"It is now abundantly clear that Pakistan has no intention of pursuing a proper and just hearing for Dr. Afridi," Paul wrote. "I will not forget Dr. Afridi, and it is time for the Senate to show it has not forgotten - or turned a blind eye to - Dr. Afridi."

Paul is a critic of many foreign assistance programs, but the Pakistan situation would appear to make for a good target - if he could ever bring the matter to a vote.

"I will continue to work tirelessly to keep this issue front and center. America should not give foreign aid to a country whose government is torturing the man who helped us kill Osama bin Laden. We should not be giving foreign aid to any country that is not clearly our ally," Paul said in a statement.

He added that he was prepared to take action to delay what little progress is being made on Senate legislative work in order to get a vote on his proposal.

The first opportunity could come if the Senate takes up legislation to provide incentives for employers to hire veterans and Reid allows votes on amendments.

Reid has opposed allowing a vote on Paul's proposal, which would cut off aid to Pakistan until Afridi is released. The vote itself could have diplomatic consequences if a large number of Senators vote with Paul to air their frustration with Pakistan. Reid has previously dismissed the Paul amendment as not germane.

Paul's proposal to cut aid could be relevant to the must-pass continuing appropriations resolution that will keep the federal government operating for the next six months. The House and Senate cannot depart for the runup to the November elections until that measure is passed.

To date, Reid has used procedural tools to prevent a vote on the Paul proposal. Paul refrained from pressing the issue to a stalemate before the August recess in part because judicial appeals in Pakistani courts were delayed.

Paul now says the delays have gone on long enough. In the letter to Reid, he noted that Afridi's defense team believes Pakistani intelligence is behind an effort to stall the proceedings without allowing the doctor to be released.